1. Field of the Invention
The present invention relates to a character output device for converting character codes inputted from an external device into dot pattern data or bit-map data and outputting the characters to a printer, a display unit, or the like based on the bit-map data.
2. Description of the Prior Art
Conventional character output devices process outline data according to input data fed from an external device to generate bit-map data and output or print a character based on the generated bit-map data, wherein the input data contain character codes and information regarding character sizes and character styles. However, it is time-consuming to process the outline data into the bit-map data. To solve such a problem, there has been proposed a character output device in which bit-map data that have once been generated are stored in a given memory area for reuse, and the stored bit-map data are read and used again when the same input data is applied, thereby eliminating the time required to process the outline data, as disclosed in Japanese Laid-Open Patent Publications Nos. 63-116192 and 63-228195. The proposed process does not need to implement the conversion from the vector data into the bit-map data at all times and hence the time required before the characters are outputted is shortened.
However, the memory used to store the bit-map data is of a predetermined storage capacity. Therefore, there is a limitation on the amount of bit-map data that can be stored in the memory. One solution to this problem is to erase initially stored bit-map data when the amount of bit-map data to be stored exceeds the storage capacity of the memory, thus allowing new bit-map data to be stored in the memory.
Characters of large size have a very large amount of bit-map data, and hence a large memory area is required to store the bit-map data, particularly if the font size of the characters is large. When such large-size characters are stored in the memory, the number of characters that can be stored in the memory is greatly reduced, and the frequency of converting vector data into bit-map data is increased. As a result, the time required until the characters are outputted is increased even though the memory stores reusable bit-map data.